Inclusion criteria :

• Male and female participants aged ≥2 and ≤17 years (or country specified age requirement) at the time of the screening visit.
• Diagnosis of rheumatoid factor-negative or rheumatoid factor positive polyarticular Juvenile Idiopathic Arthritis (JIA) subtype or oligoarticular extended JIA subtype according to the International League of Associations for Rheumatology (ILAR) 2001 Juvenile Idiopathic Arthritis Classification Criteria with at least 5 active joints as per American College of Rheumatology (ACR) definition for "active arthritis" at Screening
• Participant with an inadequate response to current treatment and considered as a candidate for a biologic disease modifying antirheumatic drug (DMARD) as per investigator's judgment

Exclusion criteria:

• Body weight <10 kg or >60 kg for participants enrolled in the 3 ascending dose cohorts, then body weight <10 kg for participants subsequently enrolled at the selected dose-regimen.
• If nonsteroidal anti-inflammatory drugs (NSAIDs) [including cyclo oxygenase-2 inhibitors (COX-2)] taken, dose stable for <2 weeks prior to the baseline visit and/or dosing prescribed outside of approved label.
• If non-biologic DMARD taken, dose stable for <6 weeks prior to the baseline visit or at a dose exceeding the recommended dose as per local labeling.
• If oral glucocorticoid taken, dose exceeding equivalent prednisone dose 0.5 mg/kg/day (or 30 mg/day) within 2 weeks prior to baseline.
• Use of parenteral or intra-articular glucocorticoid injection within 4 weeks prior to baseline.
• Prior treatment with anti-interleukin 6 (IL-6) or IL-6 receptor (IL-6R) antagonist therapies, including but not limited to tocilizumab or sarilumab.
• Treatment with any biologic treatment for pcJIA within 5 half-lives prior to the first dose of sarilumab.
• Treatment with a Janus kinase inhibitor within 4 weeks prior to the first dose of sarilumab; and treatment with growth hormone within 4 weeks prior to the first dose of sarilumab (the required off treatment periods and procedures may vary according to local requirements).
• Treatment with any investigational biologic or non-biologic product within 8 weeks or 5 half-lives prior to baseline, whichever is longer.
• Lipid lowering drug stable for less than 6 weeks prior to screening.
• Exclusion related to tuberculosis (TB).
• Exclusion criteria related to past or current infection other than tuberculosis.
• Any live, attenuated vaccine within 4 weeks prior to the baseline visit, such as varicella-zoster, oral polio, rubella vaccines. Killed or inactive vaccine may be permitted based on the Investigator's judgment.
• Exclusion related to history of a systemic hypersensitivity reaction to any biologic drug and known hypersensitivity to any constituent of the product.
• Laboratory abnormalities at the screening visit (identified by the central laboratory).
• Pregnant or breast-feeding female adolescent participants.

The above information is not intended to contain all considerations relevant to a patient's potential participation in a clinical trial.